Answer:
x = 180 - (31 + 40)
Step-by-step explanation:
Note that the angle of a straight line has a measurement of 180°
31 + x + 40 = 180°
Isolate the variable x. Note the equal sign, what you do to one side, you do to the other. Subtract 31 and 40 from both sides.
x + (40 + 31) (- (40 + 31)) = 180 (- (40 + 31))
x = 180 - (40 + 31)
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